关于K8s中Service Account的一些笔记:Pod内部如何访问K8s API Server

写在前面

学习K8s,这块官方文档的翻译的有点生涩，不太好明白。所以整理下

博文内容涉及

Service Account的简述

Service Account的Demo

官方文档:https://kubernetes.io/zh/docs/tasks/configure-pod-container/configure-service-account/

写在前面

学习K8s,这块官方文档的翻译的有点生涩，不太好明白。所以整理下

博文内容涉及

Service Account的简述

Service Account的Demo

官方文档:https://kubernetes.io/zh/docs/tasks/configure-pod-container/configure-service-account/

「 真正的坚持归于平静，靠的是温和的发力，而不是时时刻刻的刺激。」

学习环境

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get nodes NAME STATUS ROLES AGE VERSION vms81.liruilongs.github.io Ready control-plane,master 134d v1.22.2 vms82.liruilongs.github.io Ready 134d v1.22.2 vms83.liruilongs.github.io NotReady 134d v1.22.2 ┌──[root@vms81.liruilongs.github.io]-[~] └─$

Service Account 是什么？

学习Service Account之前，简单介绍下K8s的安全体系，K8s中通过一系列机制来实现集群的安全控制，其中包括API Server的认证和授(鉴)权，关于认证和授(鉴)权，感兴趣小伙伴可以看看之前的博文，我们这里简单介绍下

「关于授(鉴)权，现在用的比较多的是RBAC(Role-Based Access Control,基于角色的访问控制)的方式」

RBAC在Kubernetes的1.5版本中引入，在1.6版本时升级为Beta版本，在1.8版本时升级为GA。现在作为kubeadm安装方式的默认选项，相对于其他访问控制方式，RBAC对集群中的资源和非资源权限均有完整的覆盖。整个RBAC完全由(Role,ClusterRole,RoleBinding,ClusterRoleBinding)API对象完成，同其他API对象一样，可以用kubectl或API进行操作。可以在运行时进行调整，无须重新启动 API Server。

K8s的授权策略设置通过通过API Server的启动参数"--authorization-mode"设置。 除了RBAC外，授权策略还包括：

「关于认证机制，在K8s的认证中，如果按照集群内外认证分的话，分为集群外认证和集群内认证：」

集群外认证一般三种，也可以理解为通过kubectl或者编程语言编写的客户端API访问：

HTTP Token认证：通过一个Token来识别合法用户。

HTTPS 证书认证：基于CA根证书签名的双向数字证书认证方式(Kubeconfig文件)

HTTP Base认证：通过用户名+密码的方式认证(用户账户)，这个只有1.19之前的版本适用，之后的版本不在支持

集群内的认证也就是我们今天要讲的：Service Account对象,也叫服务账户

所以说Service Account它并不是给Kubernetes集群的用户(系统管理员、运维人员)用的,而是给运行在K8s上的Pod里的进程用的,为Pod里的进程提供认证。

比如我们要编写一个类似kubectl一样的K8s的管理工具，如一些面板工具(kubernetes-dashboard)，而且这个工具是运行在我们的K8s环境里的，那么这个时候，我们如何给这个工具访问集群做认证授权，就要用到Service Account，简写为sa,所以我们一般直接叫sa，或者服务账户

当我们创建任何一个Pod的时候，必须要有sa，否则会创建失败，如果没有显示的指定对应的sa，即服务账户，Pod会默认使用当前的命令空间的default服务账户(每个命名空间都有一个名为 default 的sa资源。)

这里要说明的是每个sa服务账户都会生成一个secret，这个secret里面包含一个token凭证。所以说sa实际认证是通过token实现的认证。(token)

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get sa default NAME SECRETS AGE default 1 67d ┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl run podcommon --image=nginx --image-pull-policy=IfNotPresent --labels="name=liruilong" --env="name=liruilong" pod/podcommon created ┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get pods podcommon -o yaml | grep serviceAccount serviceAccount: default serviceAccountName: default - serviceAccountToken: ┌──[root@vms81.liruilongs.github.io]-[~] └─$

可以使用自动挂载给Pod的default服务账户 token访问 API，但是前提是需要给default授权，对于RBAC的方式来讲，需要给角色授权，然后绑定角色。

在 1.6 以上版本中，可以通过在sa上设置automountServiceAccountToken: false来实现不给服务账号自动挂载 API token：

apiVersion: v1 kind: ServiceAccount metadata: name: build-robot automountServiceAccountToken: false ...

在 1.6 以上版本中，你也可以选择不给特定 Pod 自动挂载 API token：

apiVersion: v1 kind: Pod metadata: name: my-pod spec: serviceAccountName: build-robot automountServiceAccountToken: false ...

如果 Pod 和服务账户都指定了automountServiceAccountToken值，则 Pod 的 spec 优先于服务帐户。

下面看一下kubernetes-dashboard对sa的应用,下面是一个已经部署好的dashboard

关于kubernetes-dashboard是K8s官网提供的Kubernetes的Web UI网页管理工具，可提供部署应用、资源对象管理、容器日志查询、系统监控等常用的集群管理功能。

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get pods -o wide NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES dashboard-metrics-scraper-669c88c9d9-2qp62 1/1 Running 8 (7d11h ago) 61d 10.244.88.83 vms81.liruilongs.github.io kubernetes-dashboard-5d66bcd8fd-l22jm 1/1 Running 13 (7d3h ago) 61d 10.244.88.80 vms81.liruilongs.github.io ┌──[root@vms81.liruilongs.github.io]-[~] └─$ ┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get svc -n kubernetes-dashboard NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE dashboard-metrics-scraper ClusterIP 10.109.92.159 8000/TCP 67d kubernetes-dashboard NodePort 10.106.48.37 443:32360/TCP 67d ┌──[root@vms81.liruilongs.github.io]-[~] └─$

上面是一个我们之前部署好的面板工具，在部署的过程中，我们要主动创建一个sa(kubernetes-dashboard)，并且为这个sa授权，而后，我们的这个面板工具才具有管理K8s集群的能力

创建sa的资源文件

apiVersion: v1 kind: ServiceAccount metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard namespace: kubernetes-dashboard

查看kubernetes-dashboard sa，可以看到对应的token

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get sa NAME SECRETS AGE ...... kubernetes-dashboard 1 67d ┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get secrets NAME TYPE DATA AGE ......... kubernetes-dashboard-token-wnqqg kubernetes.io/service-account-token 3 67d ┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl describe secrets kubernetes-dashboard-token-wnqqg Name: kubernetes-dashboard-token-wnqqg Namespace: kubernetes-dashboard Labels: Annotations: kubernetes.io/service-account.name: kubernetes-dashboard kubernetes.io/service-account.uid: 8e209de5-14a0-4dd5-bd19-2264170531f5 Type: kubernetes.io/service-account-token Data ==== token: eyJhbGciOiJSUzI1NiIsImtpZCI6ImF2MmJVZ3d6M21JRC1BZUwwaHlDdzZHSGNyaVJON1BkUHF6MlhPV2NfX00ifQ.eyJpc3MiOiJrdWJlcm5ldGVzL3NlcnZpY2VhY2NvdW50Iiwia3ViZXJuZXRlcy5pby9zZXJ2aWNlYWNjb3VudC9uYW1lc3BhY2UiOiJrdWJlcm5ldGVzLWRhc2hib2FyZCIsImt1YmVybmV0ZXMuaW8vc2VydmljZWFjY291bnQvc2VjcmV0Lm5hbWUiOiJrdW.... ca.crt: 1099 bytes namespace: 20 bytes ┌──[root@vms81.liruilongs.github.io]-[~] └─$

然后对sa授权，一般通过RBAC的方式.创建角色

kind: ClusterRole apiVersion: rbac.authorization.k8s.io/v1 metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard rules: # Allow Metrics Scraper to get metrics from the Metrics server - apiGroups: ["metrics.k8s.io"] resources: ["pods", "nodes"] verbs: ["get", "list", "watch"]

然后绑定角色到sa

apiVersion: rbac.authorization.k8s.io/v1 kind: ClusterRoleBinding metadata: name: kubernetes-dashboard roleRef: apiGroup: rbac.authorization.k8s.io kind: ClusterRole name: kubernetes-dashboard subjects: - kind: ServiceAccount name: kubernetes-dashboard namespace: kubernetes-dashboard

然后pod通过serviceAccount和serviceAccountName来绑定sa，当然这两个参数指定一个就可以了。

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get pod kubernetes-dashboard-5d66bcd8fd-l22jm -o yaml | grep -C 5 serviceAccount preemptionPolicy: PreemptLowerPriority priority: 0 restartPolicy: Always schedulerName: default-scheduler securityContext: {} serviceAccount: kubernetes-dashboard serviceAccountName: kubernetes-dashboard terminationGracePeriodSeconds: 30

通过yaml文件我们可以看到，值sa为kubernetes-dashboard,当然在资源文件中，是在Deployment和Servcie中指定，

如果sa的automountServiceAccountToken或Pod的automountServiceAccountToken都未显式设置为 false，那么会为对应的 Pod 创建一个 volume，在其中包含用来访问 API 的令牌。

如果为sa对应的token创建了卷，则为 Pod 中的每个容器添加一个 volumeSource，挂载在其 /var/run/secrets/kubernetes.io/serviceaccount 目录下。

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get pod kubernetes-dashboard-5d66bcd8fd-l22jm -o yaml | grep -C 20 -i serviceAccount ........... volumeMounts: ........... - mountPath: /var/run/secrets/kubernetes.io/serviceaccount name: kube-api-access-8jlj7 readOnly: true ......... serviceAccount: kubernetes-dashboard serviceAccountName: kubernetes-dashboard ......... volumes: .......... - name: kube-api-access-8jlj7 projected: defaultMode: 420 sources: - serviceAccountToken: expirationSeconds: 3607 path: token ........ ┌──[root@vms81.liruilongs.github.io]-[~] └─$

通过配置文件可以看到,token通过卷的方式挂载到了容器里的/var/run/secrets/kubernetes.io/serviceaccount 目录，但是需要注意的是，这个token和sa对应的token在1.20版本之后进行了处理，不一样，在之前的版本中是一样的。

Service Account Demo

创建一个sa

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl create sa sa-demo serviceaccount/sa-demo created

查看对应的secret和token

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get secrets sa-demo-token-pdrs8 NAME TYPE DATA AGE sa-demo-token-pdrs8 kubernetes.io/service-account-token 3 43s ┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl describe secrets sa-demo-token-pdrs8 Name: sa-demo-token-pdrs8 Namespace: kubernetes-dashboard Labels: Annotations: kubernetes.io/service-account.name: sa-demo kubernetes.io/service-account.uid: 7003de88-803a-4dae-a6e3-d647d0517c92 Type: kubernetes.io/service-account-token Data ==== ca.crt: 1099 bytes namespace: 20 bytes token: eyJhbGciOiJSUzI1NiIsImtpZCI6ImF2MmJVZ3d6M21JRC1BZUwwaHlDdzZHSGNyaVJON1BkUHF6MlhPV2NfX00ifQ.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.sVAmtpfqFREjUCd9bkQvMuHpasXOcKYLJvVsJLLe6ufP4zs8ZVt6HqH4ylsxbmwtibNXBV9hVNEU_2X3T2enOjOSYuiyaEP4BifDQN7DmZbu2uXQCBglixaNB7ZIIPX_oQsW0ndBNonVqMSMm-ZItYDzLo-QTOxTxc5OQZ3zSBJqITAvWFlshWA7mKntNmWw6m5KunjhYZs14Lpa-NhknYS9G6ur8SKY4XdE44hzQhD7h4y01ZezZGR3IdGd3HktA5dWYTRXXr9H00odey2YtGfj40Vql3rMrdMPJOFbAozjyaWxhmSpjHVGcbXawai8znKPCdGlW4l2aRmbghovsw ┌──[root@vms81.liruilongs.github.io]-[~] └─$

编写pod资源文件，指定sa为刚才创建的sa

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl run pod-sa --image=nginx --image-pull-policy=IfNotPresent --dry-run=client -o yaml > pod-sa.yaml ┌──[root@vms81.liruilongs.github.io]-[~] └─$vim pod-sa.yaml ┌──[root@vms81.liruilongs.github.io]-[~] └─$cat pod-sa.yaml apiVersion: v1 kind: Pod metadata: creationTimestamp: null labels: run: pod-demo name: pod-demo spec: serviceAccount: sa-demo containers: - image: nginx imagePullPolicy: IfNotPresent name: pod-demo resources: {} dnsPolicy: ClusterFirst restartPolicy: Always status: {} ┌──[root@vms81.liruilongs.github.io]-[~] └─$

查看创建的pod

┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl apply -f pod-sa.yaml pod/pod-demo created ┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl get pods pod-demo NAME READY STATUS RESTARTS AGE pod-demo 1/1 Running 0 95s ┌──[root@vms81.liruilongs.github.io]-[~] └─$

对于deplay的sa修改可以直接通过set的方式设置，时间关系这里不多讲啦，文末的资源文件中有demo

下面我们来看一道Service Account相关习题,这是某一期CKA认证的一道考题

创建一个名为deployment-clusterrole且仅允许创建以下资源类型的新ClusterRole：

Deployment

StatefulSet

DaemonSet

在现有的 namespace app-team 中创建一个名为cicd-token的新 ServiceAccount。

限于 namespace app-team 中，将新的ClusterRole deployment-clusterrole绑定到新的 ServiceAccount cicd-token。

题目很简单，一般的生产我们也会涉及，指定权限创建一个集群角色，然后把这个集群角色绑定到一个新建的sa上。

# 创建集群角色 kubectl create clusterrole deployment-clusterrole --verb=create --resource=deployments,statefulsets,daemonsets # 创建服务账户 kubectl -n app-team create serviceaccount cicd-token # 绑定角色到服务账户 kubectl -n app-team create rolebinding cicd-token-rolebinding --clusterrole=deployment-clusterrole --serviceaccount=app-team:cicd-token

对sa学习，感觉kubernetes-dashboard的是一个很好的Demo。这里把面板的资源文件贴出来，感兴趣小伙伴可以研究下

# Copyright 2017 The Kubernetes Authors. # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. apiVersion: v1 kind: Namespace metadata: name: kubernetes-dashboard --- apiVersion: v1 kind: ServiceAccount metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard namespace: kubernetes-dashboard --- kind: Service apiVersion: v1 metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard namespace: kubernetes-dashboard spec: ports: - port: 443 targetPort: 8443 selector: k8s-app: kubernetes-dashboard --- apiVersion: v1 kind: Secret metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard-certs namespace: kubernetes-dashboard type: Opaque --- apiVersion: v1 kind: Secret metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard-csrf namespace: kubernetes-dashboard type: Opaque data: csrf: "" --- apiVersion: v1 kind: Secret metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard-key-holder namespace: kubernetes-dashboard type: Opaque --- kind: ConfigMap apiVersion: v1 metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard-settings namespace: kubernetes-dashboard --- kind: Role apiVersion: rbac.authorization.k8s.io/v1 metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard namespace: kubernetes-dashboard rules: # Allow Dashboard to get, update and delete Dashboard exclusive secrets. - apiGroups: [""] resources: ["secrets"] resourceNames: ["kubernetes-dashboard-key-holder", "kubernetes-dashboard-certs", "kubernetes-dashboard-csrf"] verbs: ["get", "update", "delete"] # Allow Dashboard to get and update 'kubernetes-dashboard-settings' config map. - apiGroups: [""] resources: ["configmaps"] resourceNames: ["kubernetes-dashboard-settings"] verbs: ["get", "update"] # Allow Dashboard to get metrics. - apiGroups: [""] resources: ["services"] resourceNames: ["heapster", "dashboard-metrics-scraper"] verbs: ["proxy"] - apiGroups: [""] resources: ["services/proxy"] resourceNames: ["heapster", "http:heapster:", "https:heapster:", "dashboard-metrics-scraper", "http:dashboard-metrics-scraper"] verbs: ["get"] --- kind: ClusterRole apiVersion: rbac.authorization.k8s.io/v1 metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard rules: # Allow Metrics Scraper to get metrics from the Metrics server - apiGroups: ["metrics.k8s.io"] resources: ["pods", "nodes"] verbs: ["get", "list", "watch"] --- apiVersion: rbac.authorization.k8s.io/v1 kind: RoleBinding metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard namespace: kubernetes-dashboard roleRef: apiGroup: rbac.authorization.k8s.io kind: Role name: kubernetes-dashboard subjects: - kind: ServiceAccount name: kubernetes-dashboard namespace: kubernetes-dashboard --- apiVersion: rbac.authorization.k8s.io/v1 kind: ClusterRoleBinding metadata: name: kubernetes-dashboard roleRef: apiGroup: rbac.authorization.k8s.io kind: ClusterRole name: kubernetes-dashboard subjects: - kind: ServiceAccount name: kubernetes-dashboard namespace: kubernetes-dashboard --- kind: Deployment apiVersion: apps/v1 metadata: labels: k8s-app: kubernetes-dashboard name: kubernetes-dashboard namespace: kubernetes-dashboard spec: replicas: 1 revisionHistoryLimit: 10 selector: matchLabels: k8s-app: kubernetes-dashboard template: metadata: labels: k8s-app: kubernetes-dashboard spec: containers: - name: kubernetes-dashboard #image: kubernetesui/dashboard:v2.0.0-beta8 image: registry.cn-hangzhou.aliyuncs.com/kube-iamges/dashboard:v2.0.0-beta8 #imagePullPolicy: Always imagePullPolicy: IfNotPresent ports: - containerPort: 8443 protocol: TCP args: - --auto-generate-certificates - --namespace=kubernetes-dashboard # Uncomment the following line to manually specify Kubernetes API server Host # If not specified, Dashboard will attempt to auto discover the API server and connect # to it. Uncomment only if the default does not work. # - --apiserver-host=http://my-address:port volumeMounts: - name: kubernetes-dashboard-certs mountPath: /certs # Create on-disk volume to store exec logs - mountPath: /tmp name: tmp-volume livenessProbe: httpGet: scheme: HTTPS path: / port: 8443 initialDelaySeconds: 30 timeoutSeconds: 30 securityContext: allowPrivilegeEscalation: false readOnlyRootFilesystem: true runAsUser: 1001 runAsGroup: 2001 volumes: - name: kubernetes-dashboard-certs secret: secretName: kubernetes-dashboard-certs - name: tmp-volume emptyDir: {} serviceAccountName: kubernetes-dashboard nodeSelector: "kubernetes.io/os": linux # Comment the following tolerations if Dashboard must not be deployed on master tolerations: - key: node-role.kubernetes.io/master effect: NoSchedule --- kind: Service apiVersion: v1 metadata: labels: k8s-app: dashboard-metrics-scraper name: dashboard-metrics-scraper namespace: kubernetes-dashboard spec: ports: - port: 8000 targetPort: 8000 selector: k8s-app: dashboard-metrics-scraper --- kind: Deployment apiVersion: apps/v1 metadata: labels: k8s-app: dashboard-metrics-scraper name: dashboard-metrics-scraper namespace: kubernetes-dashboard spec: replicas: 1 revisionHistoryLimit: 10 selector: matchLabels: k8s-app: dashboard-metrics-scraper template: metadata: labels: k8s-app: dashboard-metrics-scraper annotations: seccompProfile: 'runtime/default' spec: containers: - name: dashboard-metrics-scraper #image: kubernetesui/metrics-scraper:v1.0.1 image: registry.cn-hangzhou.aliyuncs.com/kube-iamges/metrics-scraper:v1.0.1 imagePullPolicy: IfNotPresent ports: - containerPort: 8000 protocol: TCP livenessProbe: httpGet: scheme: HTTP path: / port: 8000 initialDelaySeconds: 30 timeoutSeconds: 30 volumeMounts: - mountPath: /tmp name: tmp-volume securityContext: allowPrivilegeEscalation: false readOnlyRootFilesystem: true runAsUser: 1001 runAsGroup: 2001 serviceAccountName: kubernetes-dashboard nodeSelector: "kubernetes.io/os": linux # Comment the following tolerations if Dashboard must not be deployed on master tolerations: - key: node-role.kubernetes.io/master effect: NoSchedule volumes: - name: tmp-volume emptyDir: {}

API Kubernetes

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